High frequency electron discharge tubes



Jan. 16, 1962 P. c. RUGGLES 3,017,535

HIGH FREQUENCY ELECTRON DISCHARGE TUBES Filed Oct. 9, 1958 F/G./. FIG. 3.

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#24 A'r'roeNey s United Smtes Patent Omce Patented Jan. 16, 1962 assign- Lon- This invention relates to very high frequency electron discharge tubes and more specifically to output arrangements for klystron and similar discharge tubes of the kind in which very high frequency wave energy is produced in, and required to be taken from the interior of, a resonator forming part of said tube.

The invention is illustrated in and explained in connection with the accompanying drawings in which:

FIGS. 1 to 3 inclusive, which are provided for purposes of explanation, are mutually perpendicular views of a typical known klystron resonator output arrangement, and

FIGS. 4 to 6 inclusive, are mutually perpendicular views of an embodiment of this invention.

Referring to FIGS. 1 to 3 the resonator 1 of a klystron tube (it is unnecessary to show the remainder of the tube and it is accordingly not represented) is turned out of a solid block 2 of suitable material, such as nickel-iron which is then copper plated. A slot or so-called iris 3 is milled in one side of the block to provide an output path for the generated wave energy in the resonator to feed the same into a short length 4 of waveguide. A further short length 5 of similar waveguide is provided with a transverse window frame 6 in which is a glass window 7 and is joined to the waveguide length 4 by brazing by eddy current heating as indicated at 8. The parts 5 and 6 are assembled and the glass 7 is sealed in place before the parts 4 and 5 are brazed together. Generated high frequency passes through the window 7, which of course completes the vacuum tight envelope of the tube, into a further waveguide length (not shown).

This known construction has several important defects. Firstly the fact that the output wave energy has to pass through two apertures-the iris 3 and the window 7which are separated by a substantial distance, severely limits the width of the band over which the tube will operate satisfactorily. Secondly the substantial length of guide between the iris 3 and the window 7 is objectionable. In the third place the construction leads to difficulties in those numerous cases in which it is required to feed into an external waveguide cavity (not shown) which may be attached to the final output waveguide (also not shown) for the purpose of tuning the resonator 1 by pulling, for the construction obviously complicates the attachment of such an external cavity and/ or reduces its effectiveness for tuning purposes. Moreover the construction is bulky and expensive.

The present invention seeks to reduce or eliminate these defects.

The known construction is adopted, despite the defects above mentioned, because of practical difficulties which stand in the way of putting the glass window directly across the iris or slot 3. The main practical difiiculties are (1) glass sealing requires the presence of a carefully controlled oxidizing atmosphere and this, in practice, makes it difficult to seal the glass directly to the body 2, (2) the wall thickness round the edge of the slot or iris 3 is not, in practice, uniform and favorable for glass sealing and (3) where the body 2 is of solid copper its coefiicient of thermal expansion and its heat conductivity virtually prevent satisfactory glass sealing therewith.

According to this invention a klystron or similar dis- I charge tube of the kind referred to is provided with an output arrangement comprising a coupling hole in the resonator body of said tube and communicating with the resonator interior. There is a length of thin walled waveguide attached vacuum tight to said body and surrounding said coupling hole. This structure is fixed vacuum tight to the interior of the waveguide along a line on the side of the structure remote from said body.

There is a metal plate having a central aperture of approximately the same size as or slightly larger than said coupling hole fixed to said body so that said aperture is aligned with said coupling hole, and there is a frangible window and window frame structure separately fitted within said guide against said plate and fixed to the inside of said guide along the edge or corner on the side of said frame remote from said plate. In this construction the waveguide is preferably nickel, nickel-iron or nickelcobalt-iron and the plate and frame are preferably of nickel-cobalt-iron, the window in the latter and the aperture in the former being slightly larger than the coupling hole in the resonator body. The window will commonly be glass though this is not essential and in some cases ceramic windows can be used. The fixing of the frame to the inside of the guide may conveniently be accornplished by brazing by eddy current melting of a coppersilver or similar brazing alloy by inductively coupling a fiat coil carrying an alternating high frequency field to the edges of the frame inside the guide.

According to another feature of this invention a klystron or similar discharge tube of the kind referred to is provided with an output arrangement comprising a coupling hole in the resonator body of said tube and communicating with the resonator interior, a length of thin walled waveguide attached vacuum tight to said body and surrounding said coupling hole, and a frangible window and window structure frame separately fitted within and at one end of a second thin walled length of waveguide which is in turn fitted within the first mentioned length of guide and has its other end fixed vacuum tight to the interior thereof in such a position that the frame is close to but spaced from the resonator body with the window aligned with the coupling hole. Preferably in this construction a wire gasket is interposed between the frame and the adjacent resonator body. As before the window will generally be glass but ceramic windows may be preferred in some cases.

In the embodiment shown in FIGS. 4 to 6 inclusive the guide length 4 is brazed to the body 1 and the plate 9 is omitted. The window frame, pre-glassed at 7 with a slide of Kodial glass which is a boro-silicate glass which has a high melting point and is suitable for use with nickel-cobalt and the like, is mounted in a short piece 14 of thin walled waveguide which is fitted into the length 4 so that the iris-window is aligned with and close to (though slightly spaced from) the coupling-hole 3. The final brazed joint is made further back between the two guides 4 and 14 by eddy current heating of copper-silver alloy at 12. In order to preserve a good radio frequency joint near the window a wire gasket 15 is interposed between the window frame and the resonator body. It may be of gold or other suitable ductile metal and is made to stick or alloy with the copper on either side of it by pressure at a suitable temperature before the final joint at 12 is made.

I claim:

1. A vacuum discharge tube having an integral resonator body in which varying high frequency wave energy is produced, an output coupling for said tube comprising a coupling aperture in the resonator body, said aperture communicating with the interior of the resonator, a first length of waveguide, said first length being secured in vacuum sealing relationship to the body of the resonator waveguide nearer the resonator from the resonator body,

a metal plate having an aperture with bevelled edges, said plate being fitted within said second length of Waveguide adjacent the resonator body and a frangible window plate attached to said bevelled edges wherein the window plate is aligned with the coupling aperture.

2. A tube according to claim 1 including a wire gasket interposed between said metal plate and said resonator body to define a radio frequency joint therebetween.

3. The combination according to claim 1 wherein said tube is a klystron.

4. The combination according to claim 3 further including a wire gasket interposed between said metal plate and the resonator body to define a radio frequency joint therebetween.

References Cited in the file of this patent UNITED STATES PATENTS 2,454,741 McCarthy Nov. 23, 1 948 2,610,249 Fiske Sept. 9, 1952 2,617,967 Fisher Nov. 11, 1952 2,798,184 Gardner et a1 July 2, 1957 2,806,977 Carter, Jr. Sept. 17, 1957 2,815,467 Gardner Dec. 3, 1957 2,834,949 Dufiy May 13, 1958 2,847,609 Hamilton et a1. Aug. 12, 1958 

